In 'These Few Precious Days: The Final Year of Jack with Jackie', author Christopher Andersen describes how the First Lady normally turned a blind eye to JFK's cheating, but his relationship with Monroe seemed to bother her the most, reported The Independent.
According to the book, Monroe fully believed the President was going to leave his wife and marry her, reportedly telling her friend Jeanne Carmen "Can't you just see me as First Lady?"
Jackie is said to have responded, "Marilyn, you'll marry Jack, that's great. And you'll move into the White House and you'll assume the responsibilities of First Lady, and I'll move out and you'll have all the problems."
Other than the couple's relationship difficulties, the new book also claims the US President and his wife took regular amphetamine and steroid injections, administered by a man nicknamed Dr Feelgood.